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RE:DOM - Tiny but Super Fast DOM Library - Interview with Juha Lindstedt



Sometimes small is beautiful. Juha Lindstedt’s FRZR, a 4kB view library, was a nice example of that as we saw earlier. This time we’ll discuss evolution of Juha’s work - a solution known as RE:DOM.

How would you describe RE:DOM to someone who has never heard of it?


RE:DOM is a tiny UI library (~2 kB gzipped), handling only the hardest parts of managing the DOM. You could think of it as a vanilla JavaScript tool, but it’s actually really useful in almost any kind of projects – even bigger ones.

I create all my projects with it, even large single page applications. You can also render it on server-side with NO:DOM.

How does RE:DOM work?

I gave a more detailed explanation in my talk in HelsinkiJS / Frontend Finland, but basically it allows you to create HTML elements and components really easily with HyperScript syntax. Another thing it does is it helps you to keep a list of components in sync with your data. Check out examples at the RE:DOM website.

The basic idea is to use HyperScript to create HTML elements:

import { el, mount } from 'redom'

const hello = el('h1', 'Hello world!')

mount(document.body, hello)

You can also create components by defining an object with el property, which is the HTML element:

import { el, text, mount } from 'redom'

class Hello {
  constructor () {
    // how to create a component
    this.el = el('h1',
      'Hello', = text('world'),
  update (name) {
    // how to update it = name

const hello = new Hello()

mount(document.body, hello)

setTimeout(() => {
}, 1000)

Keeping lists in sync is also really easy:

import { el, list, mount } from 'redom'

// create some data
const data = new Array(100)

for (let i = 0; i < data.length; i++) {
  data[i] = {
    id: i,
    name: 'Item ' + i

// define Li component
class Li {
  constructor () {
    this.el = el('li')
  update ({ name }) {
    this.el.textContent = name

// create <ul> list
const ul = list('ul', Li, 'id')

mount(document.body, ul)

// shuffle it every second
setInterval(() => {
  data.sort((a, b) => Math.random() - 0.5)
}, 1000)

How does RE:DOM differ from other solutions?

RE:DOM doesn’t use Virtual DOM, but still allows you to define components and how to update them. For me it’s the best of both worlds: mutability gives great flexibility and performance, but defining a one-directional flow of updates is very close to VDOM-approach.

It’s also really tiny, but still does quite a lot of work. Not to mention it’s really fast. The source is also really easily readable.

Why did you develop RE:DOM?

I actually first developed FRZR, which eventually got renamed to RE:DOM. RE:DOM is a bit more clever with element creation from queries, and better designed lists. Originally I created FRZR because I was one of the Riot 2.0 early contributors and wrote a HTML element reorder method for it, which Riot lacked.

Riot’s original idea was to be a really simple UI library, which I think have got a bit out of hand. RE:DOM is basically my view of the simplest possible UI library. RE:DOM is also much more performant than Riot at the moment.

What next?

There’s some things in RE:DOM I need to think through. For example, mounted and unmounted “events” happen when attached/detached related to the parent component/element. They might be better if called when attached/detached to the DOM instead. But that’s something that needs careful approach, so it doesn’t affect the performance that much. There’s also a possibility to use Web Components instead, let’s see.

I think web standards will eventually make frameworks and UI libraries quite obsolete. That’s something recently discussed a lot in the Polymer Summit. That’s a good direction, because I think frameworks are actually the source of most of the “JavaScript fatigue” and frustration in general.

Web standards are more thought through and also a safer choice, because they will (almost) always be backwards compatible – you can’t say the same about frameworks. Abstraction usually also comes with a vendor lock-in: if you start a project with Angular for example, it’s really hard to convert the project to some other framework.

What advice would you give to programmers getting into web development?

Be open-minded about web standards and the DOM. It’s not as scary and complex as many say it is. You don’t always need a framework and you don’t always have to follow the crowd. Less is more. I recently wrote a Medium post about the subject. Even if you use some framework, you should learn how the DOM work.

Who should I interview next?

You should interview Tero Piirainen, the original author of Riot.js. Ask about web standards and simplicity in web development :)


Thanks for the interview Juha! RE:DOM looks great to me. Especially that Web Component direction sounds interesting. I think you are right in that given enough time, web standards will make a lot of the current solutions obsolete (a good thing!).

To get started with, head to RE:DOM website. Check out also the GitHub project.